oncidium everglades elegance brown spots

[Punysmurf]

Hello,

For about 8 months the bulbs on my oncidium everglades elegance have been slowly developing brown spots. currently it is affecting 2 of 5 bulbs, starting with the 2nd oldest bulb and now affecting the 3rd oldest. Both bulbs feel normal (firm). The bulb first affected started losing its leaves about 2 months ago. The oldest bulb (unaffected) has also lost its leaves. I’ve sprayed with alcohol, hydrogen peroxide, and soap spray at various points. It receives 3500 lux in a sunroom next to another oncidium which is fine and blooming right now. Does anyone know what this is and what to do, if anything? Thanks!

[Orchidtinkerer]

we need to know the temps it has been kept in and whether you have checked the roots as that should always be your first instinct when something rots.
I've had old bulbs die off in the past, probably due to stress, and the plant would carry on, discarding a bulb or two but it could be more serious and spread to the whole plant.

Let us know the state of the roots, try to keep it a bit warmer and drier to prevent rot spreading but if you see signs of dehydration don't withhold too much water.

[Ray]

If that is, indeed, spreading, your topical treatments have been of no value. It is more likely a bacterial or fungal infection that can best be treated with a systemic product.

If, after considering the conditions and checking the root quality as Orchidtinkerer suggested, everything is likely OK, you might want to consider a copper-based treatment, as they tend to be good for both bacteria and fungi.

[Punysmurf]

Thank you both for your responses! I’m not sure it could be bacterial because I would expect that it would be dead after 8 months of a bacterial infection, plus it’s not actually rotting. Everything is firm, nothing mushy. While progressing with these brown spots it has made several new bulbs and rooted nicely, so I didn’t suspect there was anything wrong with the roots. I water it the same way as all my other orchids and fertilize weekly with orchid fertilizer as per instructions. It’s potted in orchid medium with a bit of sphag at the bottom since I grow all the orchids in slotted plastic pots inside the fenestrated ceramic orchid pots. Temperature inside the sunroom ranges from 67 to 73 degrees, probably... there’s also a humidifier that keeps the humidity between 45 and 60%. There are two large windows and a grow light. I check the light each plant is getting with a lux meter, since I have plants in there ranging from a few carnivorous plants that like “full sun” vs some jewel orchids that mostly like shade. I check weekly for pests since my mother gave me a few rescues that were infested with mealybugs, and one year my macodes got spider mites (not sure how, but eradicated them with a thorough washing of each individual root and leaf and repotting). I have seen no sign of pests in this particular pot. Since I was feeling like I needed to repot anyway since the latest bulb was growing right up against the edge of the pot, I unpotted today. Roots look fine to me, no pests that I can tell, with loss of perhaps 5 roots mostly due to my rough handling getting the stuck-on bark off. Even the roots in the center looked ok to me. Some of the roots near the top have some fertilizer burn, but small areas. My list of suspects includes viruses, fungus, fertilizer burn side effects, or maybe some weird genetic problem...I’m also not sure whether losing leaves on the older bulbs is just normal for this variety. If you think the copper treatment will help, is there a brand that you think would be good? Attached please see photos of the roots today.